1. Field of the Invention
This invention relates to below the hook lifting devices, specifically to an improved lifting device capable of reaching spaces located under overhanging structures or machinery.
2. Description of Prior Art
In some instances it is necessary to lift heavy objects which are not directly accessible for the crane or hoist positioned above because of overhanging machinery or structures extending between hook of the hoisting device and the load.
To make this type of lifting operation possible, the prior art has resorted to the use of three basic types of lifting devices: an unbalanced rigid frames, an unbalanced mechanically or hydraulically adjustable frames and a balanced rigid frames.
Unbalanced rigid lifting frames utilize a principle of positioning hookup point, generally located at the end of top frame member, directly above center of gravity of the system which includes load and the frame. This type of lifting device is difficult to use because, when detached from load, such device hangs in the awkward position thus making attaching to and detaching from load unsafe and relatively difficult.
Unbalanced mechanically or hydraulically adjustable frames utilize same principle as rigid lifting frames described above except their configuration can be changed by human operator operating mechanical or hydraulic device in order to control shape of lifting frame. Although this type of lifting device is more preferable than rigid lifting frames, adjustable frames do not provide fixed predetermined positions of frame members in relation to each other thus making process of adjustment slow and tiresome. Because of mechanical and/or hydraulic moving systems such devices are relatively expensive and require additional maintenance. Hydraulically adjustable frames also have hydraulic hoses which limit their movement and create additional safety concerns.
In order to ensure correct position while being suspended, balanced rigid frames are equipped with counterweights, generally located at one end of top frame member. This type of lifting frames utilizes principle of positioning hookup point of the lifting device, generally located intermediate the ends of top frame member, directly above center of gravity of the object being lifted. Counterweight has to be heavy enough in order to balance total weight of the lifting device thus making said counterweight relatively heavy and also reducing lifting capacity of the system. In order to make such lifting frame adjustable in regard to horizontal reach, counterweight, which is difficult to reach because of its location on the upper frame member, also has to be made adjustable thus significantly complicating construction and operation of lifting device.
Other disadvantages of the prior art are associated with relatively complicated structure and frame member connections which do not allow quick assembly, disassembly and wide range adjustments often desirable for efficient use and storage of lifting devices.
In accordance with the present invention a lifting device comprises a generally orthogonal support frame having a downwardly extending telescopic leg and a forwardly extending adjustable lifting arm with a hookup point for connecting to an overhead hoisting device, a plurality of interchangeable load adapters having elongated adapter arms and a connector connecting said orthogonal frame with said adapter arms having means which human operator can manipulate to restrict or to free pivotal movement thereof thereby allowing to make connection to adapter arm rigid, when said adapter is attached to the load, or pivotal, as necessary for precise positioning and handling of lifting device prior to and after the lift. In a preferred embodiment of present invention, a counterweight assembly is attached to the rear end of adapter arm in order to balance weight of relatively heavy adapters.
In the construction of present invention, load adapter is directed towards the load and lifting arm of orthogonal support frame extends in the same direction. The lifting arm of the orthogonal support frame may thereby be connected to a suitable overhead hoisting device or a crane. The connector at the bottom of the leg of the support frame may be made free to rotate allowing easy connecting to the adapter arm of the load adapter. After load adapter is attached to the load and connector is connected to the adapter arm, the orthogonal support frame may be rotated about pivot point of the connector in the direction of the load by moving crane above and subsequently locked in a predetermined position thus completing preparation for the lift.
These and other objects of the present invention will become apparent from a reading of the following specification taken in conjunction with the enclosed drawings